UNIST Lowers Barrier to 'Dream Semiconductor' Commercialization... Proposes Theory Solving 'Post-Silicon Semiconductor' Challenge

A decisive clue has emerged to solve the "contact resistance" issue, which has been the greatest challenge in commercializing two-dimensional semiconductor materials, regarded as a "post-silicon" semiconductor material.

A research team at UNIST has proposed a theory that addresses a critical obstacle to the commercialization of next-generation semiconductors based on materials that surpass the limits of existing silicon semiconductors, drawing significant attention from the academic community. This groundbreaking research is being evaluated as a key breakthrough that could change the paradigm of future semiconductor technology.

The Korean research team has identified the reason why the theoretically predicted values of the energy barrier causing contact resistance do not match the actual experimental results. With the ability to accurately predict semiconductor performance, the development of ultra-nano semiconductor chips using two-dimensional materials is expected to accelerate.

On November 19, the team led by Professors Changwook Jeong and Sunyong Kwon at the UNIST Graduate School of Semiconductor Materials and Components announced that they had identified the cause of the discrepancy between the theoretical energy barrier that arises when a two-dimensional semiconductor material comes into contact with a semimetal called Weyl metal, and the experimental results. They also presented a new prediction formula to explain this phenomenon.

Research team, (from left) Professor Changwook Jeong, Professor Sunyong Kwon, Researcher Juwon Han (first author), Researcher Hyunwoo Lee (first author). Provided by UNIST

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The semiconductor industry has been focusing on two-dimensional semiconductor materials with atomic-scale thickness, instead of silicon, to manufacture chips with ultra-fine processes below a few nanometers (nm). However, when these two-dimensional materials are connected to conventional metal electrodes, the "contact resistance" becomes severe, impeding the flow of electrons. This is due to the high "energy barrier" (Schottky barrier) that electrons must overcome when moving from the metal to the semiconductor material.

Weyl semimetals are experimentally known as alternative materials that can lower this barrier. The problem, however, is reliability. According to existing theoretical calculations, the energy barrier is actually predicted to be high. Because the precise reason for the low energy barrier was unknown, there was significant uncertainty in practical applications.

According to this study, the difference is attributed to the "conduction band extension" phenomenon inside the molybdenum disulfide two-dimensional semiconductor material. When the electrode and semiconductor material make contact at a specific angle, the electron pathways within the semiconductor material widen, and these expanded pathways serve to lower the energy barrier.

Based on this analysis, the research team also proposed a new formula that can more accurately predict the energy barrier.

This formula takes into account not only the "conduction band extension effect" but also the "vacuum level shift effect." The vacuum level shift effect was previously considered negligible due to its small magnitude, but in thin two-dimensional semiconductors, even a small change can alter the entire barrier.

The modified formula presented by the research team accurately reproduced experimental results that could not be well explained by the conventional Schottky-Mott rule calculation formula.

Professor Changwook Jeong stated, "We have fundamentally identified the mechanism behind the formation of the energy barrier at the interface between two-dimensional semiconductors and semimetals, which existing theories could not explain. By using a more accurate theoretical calculation formula to find the optimal material combinations and structures, we can reduce trial and error in next-generation semiconductor design and significantly accelerate development speed."

Structure of semiconductor devices using two-dimensional semiconductor materials (top) and the modified energy barrier prediction formula (bottom).

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The research findings were published in the international journal ACS Nano on November 4.

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